Showing papers on "Fin published in 1999"

Review of fish swimming modes for aquatic locomotion

Abstract: Several physico-mechanical designs evolved in fish are currently inspiring robotic devices for propulsion and maneuvering purposes in underwater vehicles. Considering the potential benefits involved, this paper presents an overview of the swimming mechanisms employed by fish. The motivation is to provide a relevant and useful introduction to the existing literature for engineers with an interest in the emerging area of aquatic biomechanisms. The fish swimming types are presented, following the well-established classification scheme and nomenclature originally proposed by Breder. Fish swim either by body and/or caudal fin (BCF) movements or using median and/or paired fin (MPF) propulsion. The latter is generally employed at slow speeds, offering greater maneuverability and better propulsive efficiency, while BCF movements can achieve greater thrust and accelerations. For both BCF and MPF locomotion, specific swimming modes are identified, based on the propulsor and the type of movements (oscillatory or undulatory) employed for thrust generation. Along with general descriptions and kinematic data, the analytical approaches developed to study each swimming mode are also introduced. Particular reference is made to lunate tail propulsion, undulating fins, and labriform (oscillatory pectoral fin) swimming mechanisms, identified as having the greatest potential for exploitation in artificial systems.

Locomotor forces on a swimming fish: three-dimensional vortex wake dynamics quantified using digital particle image velocimetry.

Abstract: Quantifying the locomotor forces experienced by swimming fishes represents a significant challenge because direct measurements of force applied to the aquatic medium are not feasible. However, using the technique of digital particle image velocimetry (DPIV), it is possible to quantify the effect of fish fins on water movement and hence to estimate momentum transfer from the animal to the fluid. We used DPIV to visualize water flow in the wake of the pectoral fins of bluegill sunfish (Lepomis macrochirus) swimming at speeds of 0.5-1.5 L s(-)(1), where L is total body length. Velocity fields quantified in three perpendicular planes in the wake of the fins allowed three-dimensional reconstruction of downstream vortex structures. At low swimming speed (0.5 L s(-)(1)), vorticity is shed by each fin during the downstroke and stroke reversal to generate discrete, roughly symmetrical, vortex rings of near-uniform circulation with a central jet of high-velocity flow. At and above the maximum sustainable labriform swimming speed of 1.0 L s(-)(1), additional vorticity appears on the upstroke, indicating the production of linked pairs of rings by each fin. Fluid velocity measured in the vicinity of the fin indicates that substantial spanwise flow during the downstroke may occur as vortex rings are formed. The forces exerted by the fins on the water in three dimensions were calculated from vortex ring orientation and momentum. Mean wake-derived thrust (11.1 mN) and lift (3.2 mN) forces produced by both fins per stride at 0.5 L s(-)(1) were found to match closely empirically determined counter-forces of body drag and weight. Medially directed reaction forces were unexpectedly large, averaging 125 % of the thrust force for each fin. Such large inward forces and a deep body that isolates left- and right-side vortex rings are predicted to aid maneuverability. The observed force balance indicates that DPIV can be used to measure accurately large-scale vorticity in the wake of swimming fishes and is therefore a valuable means of studying unsteady flows produced by animals moving through fluids.

Locomotion in sturgeon: function of the pectoral fins

Abstract: Pectoral fins are one of the major features of locomotor design in ray-finned fishes and exhibit a well-documented phylogenetic transition from basal to derived clades. In percomorph fishes, the pectoral fins are often used to generate propulsive force via oscillatory movements, and pectoral fin propulsion in this relatively derived clade has been analyzed extensively. However, in the plesiomorphic pectoral fin condition, exemplified by sturgeon, pectoral fins extend laterally from the body in a generally horizontal orientation, have been assumed to generate lift to balance lift forces and moments produced by the heterocercal tail, and are not oscillated to generate propulsive force. The proposal that pectoral fins in fishes such as sturgeon generate lift during horizontal locomotion has never been tested experimentally in freely swimming fishes. In this paper, we examine the function of pectoral fins in sturgeon swimming at speeds from 0.5‐3.0L s -1 , where L is total body length. Sturgeon were studied during steady horizontal locomotion as well as while sinking and rising in the water column. Pectoral fin function was quantified using three-dimensional kinematics to measure the orientation of the fin surface, digital particle image velocimetry (DPIV) was used to describe flow in the wake of the fin and to estimate force exerted on the water, and electromyography was used to assess pectoral fin muscle function. Sturgeon (size range 25‐32 cm total length) swam horizontally using continuous undulations of the body with a positive body angle that decreased from a mean of 20 ° at 0.5 L s -1 to 0 ° at 3.0 L s -1 . Both the angle of the body and the pectoral fin surface angle changed significantly when sturgeon moved vertically in the water column. Three-dimensional kinematic analysis showed that during steady horizontal swimming the pectoral fins are oriented with a negative angle of attack predicted to generate no significant lift. This result was confirmed by DPIV analysis of the pectoral fin wake, which only revealed fin vortices, and hence force generation, during maneuvering. The orientation of the pectoral fins estimated by a two-dimensional analysis alone is greatly in error and may have contributed to previous suggestions that the pectoral fins are oriented to generate lift. Combined electromyographic and kinematic data showed that the posterior half of the pectoral fin is actively moved as a flap to reorient the head and body to initiate rising and sinking movements. A new force balance for swimming sturgeon is proposed for steady swimming and vertical maneuvering. During steady locomotion, the pectoral fins generate no lift and the positive body angle to the flow is used both to generate lift and to balance moments around the center of mass. To initiate rising or sinking, the posterior portion of the pectoral fins is actively moved ventrally or dorsally, respectively, initiating a starting vortex that, in turn, induces a pitching moment reorienting the body in the flow. Adjustments to body angle initiated by the pectoral fins serve as the primary means by which moments are balanced. Summary

Air-Side Heat Transfer and Friction Correlations for Plain Fin-and-Tube Heat Exchangers With Staggered Tube Arrangements

Abstract: This paper deals with heat exchangers having plain fins on a staggered array of circular tubes. Correlations are developed to predict the air-side heat transfer coefficient and friction factor as a function of the Reynolds number and geometric variables of the heat exchanger such as tube diameter, tube pitch, fin spacing, etc. A multiple regression technique was used to correlate 47 sets of heat exchanger data to develop the heat transfer and friction correlation. The correlations are applicable to heat exchangers having small diameter tubes (or large tube pitch to tube diameter ratio), whose performance previous correlations failed to predict adequately. The heat transfer correlation applicable to three or more row configuration predicts 94% of the data within {+-}20%, and the heat transfer correlation applicable to one- or two-row configuration predicts 94% of the data within {+-}20%. The friction correlation predicts 90% of the data within {+-}20%.

Pin fin heat sink and pin fin arrangement therein

Abstract: A pin fin heat sink having mixed geometry pin fin configurations is presented. The mixed geometry pin fin configuration are designed to optimize the positive attributes of each individual pin fin geometry to provide a low cost overall system and provide better system performance in high flow rate systems. In an exemplary embodiment, the pin fin heat sink comprises a base surface having a plurality of pin fins perpendicular to and protruding therefrom. The plurality of pin fins actually comprises a plurality of pin fins having a first configuration and a plurality of pin fins having a second configuration. The second configuration pin fins are intended to streamline any turbulence created by the first configuration pin fins which are located upstream of the second configuration pin fins. Preferably, the first configuration comprises substantially circular shaped pin fins and the second configuration comprises substantially elliptical shaped pin fins.

Optimization of circular fins with variable thermal parameters

Abstract: The optimization of rectangular profile circular fins with variable thermal conductivity and convective heat transfer coefficients is discussed. The linear variation of the thermal conductivity is considered to be of the form k = ka(1+β(T−Ta)), and the heat transfer coefficient is assumed to vary according to an exponential function with the distance from the bore of the form h = hb exp (γ(r−rb)\(re−rb)). The nonlinear conducting–convecting–radiating heat transfer equation is solved by the differential transformation method. The effective of convective–radiative heat transfer at the fin tip is considered. It is shown that, considering the thermal conductivity and heat transfer coefficient are both constant, for a given fin volume, the optimum fin length is almost independent of the fin base temperature for pure convection. However, for both convection–radiation and pure radiation, the length of the optimum fins for higher temperatures is shorter than the length of the fins with lower temperatures.

Effect of strip location on the air-side pressure drop and heat transfer in strip fin-and-tube heat exchanger

Abstract: This work discusses about the pressure drop and heat transfer characteristics of a plain fin, a strip fin and combinations thereof in the fin-and-tube heat exchanger. Experimental apparatus and test algorithm using scale-up model fin geometry are discussed. The present work uses the electric heaters inside of the tube as the heating source to simulate the hot water loop in the wind tunnel test. The test results of the plain and strip fins are compared with the existing correlation and experimental data. It was found that a hybrid fin, plain fin at front row and strip fin at rear row, was more effective to enhance the heat transfer than that of the whole strip fin at the same fan power.

Stackable heat sink for electronic components

Abstract: A stackable heat sink having a core shaft in heat-engaging relation with a semiconductor device and a plurality of individual thin fins having an opening for receiving the core shaft in press fit relation so that a plurality of the fins, when mounted on the shaft, define a plurality of air passageways and the fins and shaft efficiently transfer heat away from the semiconductor device and into the surrounding atmosphere. In an improved version of the heat sink, the heat-dissipating fins may be corrugated so as to increase the surface area of each individual fin without increasing its perimeter. A heat pipe may be used in conjunction with the core shaft or base of the heat sink so as to facilitate heat transfer away from the electronic component. An improved heat sink may also include a base having a plurality of openings and a small fan connected to the portion of the base with the openings, so as to direct air across and between adjacent fins.

Performance of Dehumidifying Heat Exchangers With and Without Wetting Coatings

Abstract: Limited previous work has shown that use of special hydrophilic coatings will provide lower air pressure drop in finned tube heat exchangers operated under dehumidifying conditions. However, no detailed work has been reported on the effect of different coating types, or different fin surface geometries on the wet pressure drop. In this study, wind tunnel tests were performed on three different fin geometries (wavy, lanced, and louver) under wet and dry conditions. All dehumidification tests were done for fully wet surface conditions. For each geometry, the tests were performed on uncoated and coated heat exchangers. For all three fin geometries, the wet-to-dry pressure drop ratio was 1.2 at 2.5 m/s frontal air velocity. The coatings have no influence on the wet or dry heat transfer coefficient. However, the wet surface heat transfer coefficient was 10 to 30% less than the dry heat transfer coefficient, depending on the particular fin geometry. The effect of the fin press oil on wet pressure drop was also studied. If the oil contains a surfactant, good temporary wetting can be obtained on an uncoated surface; however, this effect is quickly degraded as the oil is washed from the surface during wet operation. This work alsomore » provides a critical assessment of data reduction methods for wet surface operation, including calculation of the fin efficiency.« less

Effects of Waffle Height on the Air-Side Performance of Wavy Fin-and-Tube Heat Exchangers

Abstract: An experimental study was carried out to examine the effects of the waffle height, including three different values of waffle height-1.18, 1.32, and 1.58 mm-on the heat transfer and friction characteristics of typical fin-and-tube heat exchangers having wavy fins. A total of 13 samples of heat exchangers, nine of them having wavy fins and the other four having plain fin configurations, were tested. The test results indicated that the effect of waffle height on the heat transfer enhancement ratio, compared to the plain-fin counterpart, is pronounced only for smaller fin pitch and larger waffle height, while its effect on the pressure drop is considerably significant throughout the test range.

Pectoral fin size in a fish species with paternal care : a condition-dependent sexual trait revealing infection status

Abstract: Summary 1. The three-spined stickleback, Gasterosteus aculeatus L., is a territorial fish with exclusive male parental care. Males oxygenate the eggs with fanning movements of their pectoral fins. The present authors investigated whether the apparent sexual differences in the functional demands of the pectoral fins have resulted in sexual differences in fin size. If males have relatively larger pectoral fins, females may use this as a signal to aid their mate choice for good fathers. Therefore, further objectives were to study the condition-dependency of relative pectoral fin size in males and the relationship with male parasite load. 2. Reproductively active males possessed relatively larger pectoral fins than females in both wild-caught and laboratory-bred fish. 3. In the field, caring males with relatively large pectoral fins were in better physical condition and had more food in their stomachs. 4. Relatively small pectoral fins and poor body condition were associated with infection by the intestinal parasite Pomphorhynchus laevis (Acanthocephala), the prevalent parasite species in the study population.

Constructal Trees of Convective Fins

Abstract: This paper extends to the field of convective heat transfer the constructal theory of optimizing the access of a current that flows between one point and a finite-size volume, when the volume size is constrained. The volume is bathed by a uniform stream. A small amount of high-conductivity fin material is distributed optimally through the volume, and makes the connection between the volume and one point (fin root) on its boundary. The optimization proceeds in a series of volume subsystems of increasing sizes (elemental volume, first construct, second construct). The shape of the volume and the relative thicknesses of the fins are optimized at each level of assembly. The optimized structure emerges as a tree of fins in which every geometric detail is a result of minimizing the thermal resistance between the finite-size volume and the root point (source, sink). Convection occurs in the interstitial spaces of the tree. The paper shows that several of the geometric details of the optimized structure are robust, i.e., relatively insensitive to changes in other design parameters. The paper concludes with a discussion of constructal theory and the relevance of the optimized tree structures to predicting natural self-organization and self-optimization.

High efficiency modular OLF heat exchanger with heat transfer enhancement

Abstract: A high efficiency modular OLF heat exchanger with heat transfer enhancement is disclosed. The OLF heat exchanger has an oblique louver fin provided with oblique strips. The oblique louver fin thus effectively forms transverse and longitudinal vortexes in a main gas flow while breaking the boundary layer of the gas flow, thus having an improved heat transferring effect. In the OLF heat exchanger, a plurality of flat tubes are assembled with two opposite header pipes, thus forming a module. The OLF heat exchanger is thus manufactured while easily permitting changes in its size and heat exchanging capacity by assembling a selected number of modules into a single body using a plurality of header pipe sockets. The oblique strips violently mix the gas flow and thereby further improve the heat transferring effect of the louver fin. The oblique louver fin thus has advantages expected from typical louver fins with swirlers and typical offset strip fins with swirlers.

Influence of Flow Velocity and Fin Spacing on the Forced Convective Heat Transfer from an Annular-Finned Tube.

Abstract: The evaluation of convective heat transfer from fins to the air has been carried out in the case of annular fins subjected to an air flow parallel to the fin surface. The fin cooling is studied using infrared thermography. The thermal balance in a fin during its cooling process allows us to obtain the expression of the heat transfer coefficient from the temperature time evolution of the fin. Besides, the Particle Image Velocimetry allows us to obain the flow field in the mid-plane between two fins. The influence of the air flow velocity and of the fin spacing on the convective exchanges is studied. The tests have been carried out for Reynolds numbers(based on the shaft diameter and the air flow velocity)between 2550 and 42000, for different fin spacings. All the tests are correlated by an equation, expressing the mean Nusselt number on the fin as a function of the dimensionless fin spacing and of the Reynolds number.

Folded fin heat sink and a heat exchanger employing the heat sink

Abstract: A heat sink is disclosed for use with a heat exchanger employing a circular fan which forces air in a volute path about a central axis. The heat sink includes a plurality of heat exchanging sections disposed in the path about the axis. Each heat exchanging section includes a thermally conductive sheet folded into alternating ridges and troughs defining generally parallel spaced fins. The heat exchanging sections are oriented such that the fins of each section are at an angle to the fins of an adjacent section.

Influence of Flow Velocity and Fin Spacing on the Forced Convective Heat Transfer from an Annular-Finned Tube

Abstract: The evaluation of convective heat transfer from fins to the air has been carried out in the case of annular fins subjected to an air flow parallel to the fin surface. The fin cooling is studied using infrared thermography. The thermal balance in a fin during its cooling process allows us to obtain the expression of the heat transfer coefficient from the temperature time evolution of the fin. Besides, the Particle Image Velocimetry allows us to obain the flow field in the mid-plane between two fins. The influence of the air flow velocity and of the fin spacing on the convective exchanges is studied. The tests have been carried out for Reynolds numbers(based on the shaft diameter and the air flow velocity)between 2550 and 42000, for different fin spacings. All the tests are correlated by an equation, expressing the mean Nusselt number on the fin as a function of the dimensionless fin spacing and of the Reynolds number.

Time-dependent calculation procedure for fully developed and developing flow and heat transfer in louvered fin geometries

Abstract: Previous studies by Zhang et al., have shown the importance of including unsteady effects in the numerical simulation of air-side flow and heat transfer in compact heat exchangers. In this paper the authors describe a computer program for the time accurate flow and heat transfer calculations in an array of louvered fins. Preliminary calculations, ranging from the low Reynolds number laminar to the transitional regime, are performed for both fully developed and developing flow and heat transfer. The results capture the duct flow and lower directed flow regimes observed in earlier flow visualization studies. Preliminary results of spatial propagation of transition from steady to unsteady in a multilouvered fin array are also presented. In the transitional regime the effect of large-scale vorticity on heat transfer is captured with clarity. In view of the difficulties associated with detailed experimental flow and heat transfer measurements, the current computer program provides a powerful tool for understanding the fundamental flow structure and its effect on heat transfer in louvered fit heat exchangers.

Stove pipe thermoelectric generator

Abstract: A stovepipe thermoelectric generator. The unit fits in a stovepipe of a coal or wood stove. At least one thermoelectric module is sandwiched between a hot side fin unit with fins extending into the flow of exhaust gases and a cold side fin unit with fins cooled by forced room air. A damper controls exhaust gas flow through a heat chamber, directing the exhaust gas through a generating side and a bypass side depending on a temperature indication. This prevents heat damage to the thermoelectric module. At least one fan is provided to force room air through cooling fins of the cold side fin unit An electric circuit is described for providing power for the fan and providing additional electric power for purposes such as charging a battery.

Zipper fins for plastic bags

Abstract: A plastic bag comprises first and second panels each having a top, a bottom, and first and second opposing sides. The first and second panels are joined to each other along their respective bottoms, their respective first opposing sides, and their respective second opposing sides. The plastic bag includes a zipper having a male and female track. The male track includes a male profile and a first fin, in which the first fin is affixed to the first panel in proximity to the top of said first panel. The female track includes a female profile and a second fin, in which the second fin is affixed to the second panel in proximity to the top of said second panel. The male and female profiles having complementary cross-sections. The inventive fins comprise a first resin and, optionally, a second resin which, along with the fins seals, are able to withstand greater forces and more adverse conditions. At least one of the fins comprises a first resin having a polydispersity of about 1 to about 4, a melt index of about 0.2 to about 20, and a melt flow ratio of about 12 to about 35. The second resin, if used, may either be coextruded or blended with the first resin.

Thermoplastic material melting unit having high throughput and heating capacity

Abstract: A thermoplastic material melting unit (10) including various grid and reservoir configurations designed, for example, to optimize flow rate, melt rate and residence time within a melting unit. A main embodiment includes a supply hopper (12) connected with a liquid reservoir (18) having a plurality of heat exchanging elements, such as fins (50) extending upward from its bottom wall. A melting grid (16) is generally disposed between the supply hopper (12) and the reservoir (18) and includes both upwardly and downwardly extending heated fins (52, 60). The downwardly extending fins (52) intermesh with the upwardly extending fins (50) of the reservoir (18). Additional embodiments of melting grids and heat exchange devices for melting solid thermoplastic material include bare element configurations, angled fin configurations and slotted fin configurations.

Dental-restoration light-curing system

Abstract: A blue-light polymerizing system comprises a xenon arc lamp in which its sapphire window includes a blue-bandpass filter coating. This eliminates any external color filters that would otherwise be necessary for the polymerization of dental composite materials in a patient's mouth. The blue-bandpass filter coating causes the xenon arc lamp to heat an extra 10° C. higher than would otherwise be the case. So a special anode heatsink is fitted in which the front and back halves of each radial fin have been separated, and one of these groups of separated fins has been tilted off normal. Such changes the otherwise laminar airflow through the anode heatsink fins to a turbulent flow that is better able to collect heat and carry it off.

Heat sink with arc shaped fins

Abstract: A heat exchanger and a method of manufacturing the heat exchanger is disclosed for dissipating heat from a heat generating component. The heat exchanger comprises a thermally conductive base in thermal communication with the component, a plurality of thermally conductive plate fins affixed to the base wherein the plate fins define a fin field and channels, and fluid control for controlling the fluid flow within the fin field. The individual fins of the heat exchanger comprise an arc shape with diametrically opposed legs extending vertically downward from each end of the fins. The individual fins are comprised of thermally conductive material affixed to and in thermal communication with the base. The individual fins are arcuately shaped sections separated by arcuately shaped channels. The fins, together with the channels and base form a fin field having an inlet region, a middle region and an outlet region. Additionally, the fins may comprise a plurality of orifices, slots and/or apertures to enhance cross channel fluid communication, and/or textured surface regions in the form of surface anomalies for disrupting formation of a boundary layer along said fins.

Pressure drop coefficients for elliptic and circular sections in one, two and three-row arrangements of plate fin and tube heat exchangers

Abstract: The objective of the present work is the experimental determination of pressure drop coefficients (loss coefficients) for elliptic and circular sections in one, two and three-row arrangements of plate fin and tube heat exchangers. The experiments permitted to correlate the dimensionless loss coefficient with the flow Reynolds number in the rectangular channel formed by the plate fins. The experimental technique consisted of the measurement of the longitudinal pressure distribution along the flow channel, for several values of air mass flow rate. The total number of data runs, each one characterized by the flow Reynolds number, was 216. The present geometry is used in compact heat exchangers for air conditioning systems, heaters, radiators, and others. Also, it is verified the influence of the utilization of elliptic tubes, instead of circular ones, in the pressure drop. The measurements were performed for Reynolds numbers ranging from 200 to 1900.

Enhanced customizable surfboards with adjustable fins and methods for making the same

Abstract: A surfboard includes a body, a fin, a chamber disposed in the body, and a fastener. The fin is receivable in the chamber and projects from the body at a cant when received in the chamber. The chamber and the fastener may be components of a fin box disposed on the body of the surfboard. The chamber is configured so that the fin is adjustable in a variety of cants. The chamber may be configured to allow a foot of the fin to pivot within the chamber. When the fin is positioned in a desired cant, the fastener secures the fin in the chamber at the desired cant. To adjust the cant, the fastener is actuated to release the fin, the fin is repositioned at another cant, and the fastener is actuated to secure the fin at the new desired cant. This adjustment of the fin may be repeated any number of times.